It is desirable in tenter frames to have a driven sprocket for each of the opposed runs of chain. Thus, a main drive at the exit or delivery end of the tenter frame may be provided in such a way that a single motor drives both chain sprockets through a splined or other positive mechanical connection to insure maintaining the opposed tenter clips in proper register. In other words, the travel of the opposed runs of chain must be coordinated so that one does not advance with respect to the other during the web carrying process. Because of the splined connection, some adjustment in transverse spacing between the chains is permitted at the delivery end of the tenter frame. It is also important that the drive for the tenter frame be controlled at a single end, otherwise a control at the other end may take over and have a tendency to cause undesirable variations in speed and control of the tenter frame.
A problem in controlling the slack in tenter chains, which have heretofore usually had a spring loaded sliding mounting and the like on the rails, has persisted although the problem has been addressed in a number of ways in an effort to find a solution. Tenter frames presenly in service utilize substantially zero or minimal tension at this point. Efforts to increase the tension in the chain to avoid chattering or excessive tangential movement necessarily have the undesirable affect of increasing the tension on opposed portions of the chain causing excessive wear and maintenance on the various moving and auxiliary parts of the tenter frame.
With the advent of roller clips and the desirability of using chains of greater length accompanied often by higher speeds for carrying the clips, the problem of chattering of the chains and tenter clips opposite the drive points at the delivery end of the tenter has become aggravated. One of the major advantages of utilizing roller clips is the possibility of running the chains and clips on the rails without grease or oil, deriving many advantages therefrom, however, the impact upon the roller bearings, accompanied by the chattering action of the chain when driven near zero or at low tension with the tendency for tangential movement of the tenter clips results in impact loads which are especially harmful to bearings, causing excessive wear and roughness of operation.
It is particularly desirable to employ the drive means illustrated herein in connection with roller mounted clips and rails which have suitable connection for avoiding uneven movement of the tenter clips as disclosed in co-pending application Ser. No. 196,257, filed Oct. 14, 1980, in the name of Hans H. Richter for TENTER FRAME WITH ROLLER CLIP.
Such roller bearing clip mechanisms are especially desirable for use in film and textile tenters with which the invention hereof is described, however, the apparatus and method hereof has application to tenter frame mechanisms generally including the standard sliding variety of tenter clip devices.
This application is an improvement upon the aforesaid application, Ser. No. 196,257, filed Oct. 14, 1980, and the disclosure thereof is incorporated and made a part hereof by reference.
Accordingly, it is an important object of this invention to provide an auxiliary drive associated with each of the sprockets carried at the entrance ends of each of the chains of a tenter frame to remove slack and avoid chattering in the chains of the tenter frame.
Another important object of the invention is to provide an auxiliary drive system at the entrance end of a tenter frame in such a way that the auxiliary drive is controlled responsive to the main drive at the delivery end of the tenter frame.
Still another important object of the invention is to provide an auxiliary drive mechanism for removing the slack in the tenter clip carrying chains of a tenter frame in such a fashion as to reduce the tension occurring at the point of maximum tension in the chains while assuring sufficient tension at the pull side runs that effectively control the web at the entrance portion of the tenter frame.